Many investigations have been made on catalytic systems that permit uniform dimerization of lower monoolefins such as ethylene, propylene, and butene. As the catalysts, Ziegler-type catalysts having transition metals as central catalyst component are usually superior in dimer selectivity of the lower monoolefins. In particular, satisfactory results have been obtained in dimerization activity and selectivity with a catalyst obtained from a mixture of a nickel compound and organic aluminum halide.
Investigations have also been made on catalytic systems containing organic phosphorus compounds as third additives to the above mentioned catalytic component. It is known that these additives affect on catalytic activity and product selectivity. As these catalytic system containing the organic phosphorus compounds, 1 Japanese Patent Publication No. 46-34007 discloses a catalytic system comprising .pi.-allyl-type nickel complex, an organic aluminum halide and an organic phosphine. 2 Japanese Patent Publication Nos. 48-30241 and 50-30041 disclose catalytic systems comprising organic phosphine complexes of nickel represented by (R.sub.4 P).sup.+ (R.sub.3 PNiX.sub.3).sup.- and NiX'.sub.2 (PR'.sub.3).sub.2, respectively, where R represents hydrocarbyl group or hydrogen, X and X' each represents chlorine, bromine or iodine, and R' represents alkyl group. In addition, 3 Japanese unexamined Patent Publication No. 57-169433 discloses a catalytic system where halogenated phenol and water are added as fourth additives to a nickel compound, alkylaluminum and a trivalent phosphorus compound. It is disclosed to use, as the trivalent phosphorus compound in this case, trivalent organic phosphite compounds such as triethyl phosphite, tri-n-octyl phosphite, and triphenyl phosphite other than the above mentioned organic phosphine.
A large volume of C.sub.4 fraction are obtained during thermal cracking of naphtha or catalytic cracking of heavy oils. n-butenes extracted and separated from the fraction may be dimerized to improve octene yields. 4 Japanese Patent Publication 3-42249 discloses an approach to improve the octene yields with a catalytic system comprising a nickel compound selected from the group consisting of nickel salts of higher mono- or di-carboxylic acid having from 5 to 20 carbon atoms and a coordination complex of organic phosphine and nickel halide, an organic aluminum compound, and hydrogen.
Product olefins such as octenes obtained by the above mentioned dimerization method of lower olefins are hydroformylated and hydrogenated to alcohols having 9 carbon atoms (hereinafter, referred to as "INA") . These alcohols are known to be advantageously used as materials of plasticizers for polyvinyl chloride resin (British Patent No. 789,777and Japanese Patent Publication No. 61-15849, etc.).
As mentioned above, various organic phosphorus compounds have been proposed as ligands used for dimerization reaction. These compounds are, however, not always satisfactory in view of industrial applications. That is, the catalytic systems disclosed in the above 1 Japanese Patent Publication No. 46-34007 have faults that they are extremely unstable to air and thus have difficulty to deal with and that synthesis of the catalysis is complex. In addition the catalytic systems disclosed in the above 2 Japanese Patent Publication No. 48-30241 involve troublesomeness when used industrially since a complex nickel complex should be synthesized separately.
Dimerization products in the case that reaction material is propylene or butene are obtained normally as a mixture of straight-chain and various branched compounds. In the case that these products may be for the above mentioned alcohol for plasticizers, the lower the degree of branching of the product used is, the higher the reaction rate in hydroformylation is that is useful as a method for synthesizing alcohols for plasticizers, and the lower the degree of branching of resultant alcohol. The alcohol having a lower degree of branching offers higher performance such as heat resistance and cold temperature flexibility, required for alcohols for plasticizers. It is thus an industrial challenge to develop a method of selectively producing dimerized olefins having the lower degree of branching. With this respect, the catalytic systems disclosed in the above 3 Japanese unexamined Patent Publication No. 57-169433 and 4 Japanese Patent Publication No. 3-42249, which are high in dimerization activity, are not suitable for applications in the above mentioned field because the resultant product has a higher ratio of olefin with two branches.
There have been proposed catalytic systems with promoters of various organic phosphorus compounds as the dimerization catalysts for the lower olefin. The existing catalytic systems are not always satisfactory to be used industrially by the considerations of catalyst stability, synthetic methods, catalytic efficiency, and product selectivity and some problems still remain unsolved.
An object of the present invention is to apply the above mentioned dimerized products of the lower olefin to alcohols for plasticizers which are valuable in industrial usage.
The principal aim of the present invention is therefore to develop a dimerization catalyst which is superior in catalytic efficiency and selectivity to a target product, and to develop a method of producing alcohol especially suitable for plasticizers with the resultant dimerization products that has lower degree of branching.